Studies will be carried out to measure several metabolic parameters in DMBA-induced tumors of the mammary glands of rats. Levels of prostaglandins, arachidonic acid, cyclic AMP, cyclic GMP, guanylate cyclase, adenylate cyclase, cyclic nucleotide phosphodiesterase, and phospholipase A will be measured. The objective of this work will be to search for the primary problem which is causing an abnormal proliferation of the mammary gland tissue.